Enhancement of IR photoluminescence of β‐FeSi₂ nanocrystals by Cu‐doping and study of its mechanism

Abstract

We have investigated the IR photoluminescence (PL) behavior of Cu‐doped β‐FeSi2 nanocrystals (β‐NCs) embedded in Si layers. The diffusion rate of Cu atom was controlled by annealing. The most appropriate condition brought the largest intensities of both the intrinsic A band emission at 0.803 eV by 214% and the acceptor related C band emission at ∼0.75 eV by 582% in comparison with those of non‐doped β‐NCs. Rutherford backscattering spectrometry (RBS) revealed increase of Cu atoms in the Si layer with β‐NCs with increasing the anneal duration. The C band enhancement surely is originated from increase of a density of state at acceptor levels relating to increase of Cu in β‐lattice. Photocarrier injection PL measurements (PCI‐PL) reveal that the enhancement of the A band emission may be attributed to a controlled migration process of holes with a repeated trap process due to Cu‐doping into the Si phase. This dynamic condition leads to an increase of valence band offset at the β‐NCs/Si heterointerfaces where the migration of holes from the β‐NCs to Si is prevented, so that a radiative recombination rate can be enhanced. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhancement of photoluminescence from Cu-doped β-FeSi₂/Si heterostructures

“…In the Cu-doped samples, we obtained two time constants of 1=88 s and 2=21 s which are longer than 1=27 s and 2=10 s found in the non-doped samples. Such a longer time constant of 1=88 s may be originated from a repeated trap process of positive holes during migration in n-type Si substrates as well as that observed in the -FeSi2 nanocrystal/Si composite phase [5]. We think that PL enhancement observed in Fig.…”

“…This PCI-PL measurements indicate that photocarrier injection can be succeeded through the -FeSi2 thin film/n-Si heterojunction as well as in a -FeSi2 nanocrystal/Si composite phase. The time constant  can be obtained from measurements of the frequency dependence of  was analyzed by the following equation [5]. Actually the following relation can be seen in Fig.…”

Enhancement of photoluminescence from Cu-doped β-FeSi2/Si heterostructures

“…In the Cu-doped samples, we obtained two time constants of 1=88 s and 2=21 s which are longer than 1=27 s and 2=10 s found in the non-doped samples. Such a longer time constant of 1=88 s may be originated from a repeated trap process of positive holes during migration in n-type Si substrates as well as that observed in the -FeSi2 nanocrystal/Si composite phase [5]. We think that PL enhancement observed in Fig.1 is attributed to a repeated trap process of holes in the -FeSi2 thin film/Si heterostructures because this dynamic process can contribute to reduction of number of holes going out from -FeSi2 thin films and adapts to increase of the radiative recombination rate of electrons and holes at the thin film.…”

Enhancement of photoluminescence from nanocrystal β-FeSi2/SiO2 composite and relaxation of thermal quenching

“…Photocarrier injection photoluminescence (PCI-PL) 25,37,41) is related to the radiative recombination of minority carriers optically injected at the back surface of Si, as shown in Fig. 2(a).…”